In general, various source materials such as crude oil are often present as a mixture of numerous chemicals. Therefore, the source materials themselves are hardly used in industries, but are generally separated into respective compounds that are used in industries. A distillation process is representative of chemical processes for separating a mixture.
In general, the distillation process serves to separate the mixture into two components: a high boiling point component and a low boiling point component. Therefore, the distillation columns whose number (n−1) is smaller than the number (n) of components in the mixture to be separated by 1 are used. That is to say, a process for separating a three-component mixture has mainly used a structure in which two distillation columns are continuously operated on site in conventional distillation industries.
A conventional distillation process for separating a three-component mixture is shown in FIG. 1.
The conventional distillation process uses a two-column system in which a lowermost boiling point component (D) is separated in a first column 11, and a middle boiling point component (S) and a high boiling point component (B) are separated in a second column 21.
In a conventional two-column distillation system, a compositional profile of acrylic acid in a first column is shown in FIG. 2. As shown in FIG. 2, the middle boiling point component (S) may be generally remixed in a lower section of the first column.
The above-described conventional distillation process can easily control a composition of a product, but the middle boiling point component is remixed in the first distillation column. Therefore, a thermodynamic efficiency in the distillation column is degraded, resulting in unnecessary consumption of energy.
In order to solve these problems, much research on a new distillation structure has been conducted. A representative example of improving a separation efficiency using a thermally coupled structure may be a structure of a Petlyuk distillation column as shown in FIG. 3. The Petlyuk distillation column is arranged in a structure in which a preliminary separator 12 and a main separator 22 are thermally coupled. Therefore, a low boiling point component and a high boiling point component are primarily separated in the preliminary separator, and then flow to a feed plate of the main separator through a column-top portion and a column-bottom portion of the preliminary separator. Thereafter, the low boiling point, middle boiling point, and high boiling point components are separated in the main separator. This structure has high energy efficiency since a distillation curve in the Petlyuk distillation column is similar to an equilibrium distillation curve. However, the design and operation of a process are not easy, and the balance of pressure in the distillation column is particularly difficult to adjust.
In order to solve the problems regarding the Petlyuk distillation column, a dividing wall distillation column (DWC) has been proposed. A thermodynamic aspect of the DWC is similar to that of the Petlyuk distillation column, but a structural aspect is different from that of the Petlyuk distillation column in that a dividing wall is installed in a distillation column to integrate the preliminary separator of the Petlyuk distillation column in the main separator. Such a structure is highly advantageous in that operations are easily performed since the problems regarding the balance between the preliminary separator of the Petlyuk distillation column and the main separator are naturally solved and thus operations are simple, and the investment costs may also be significantly reduced since two types of distillation columns are integrated into one.
The following Documents 1 and 2 disclose a conventional technique associated with the distillation of acrylic acid.
Document 1 discloses a method of distilling and separating pure (meth)acrylic acid from a mixture. That is to say, a distillation device, which includes a thin film evaporator, a condenser, a baffle unit, and a connection unit for connecting the thin film evaporator to the condenser, is used to distill and separate pure (meth)acrylic acid from a mixture that includes (meth)acrylic acid and a dimer and oligomer of the (meth)acrylic acid and does not substantially include an aldehyde or a component having a lower boiling point than the (meth)acrylic acid.
Document 2 discloses a method of purifying a (meth)acryl monomer through distillation. The method known in the prior art includes purifying a (meth)acryl monomer, selected from (meth)acrylic acid and esters thereof, from a liquid containing a (meth)acrylic acid monomer by distilling the liquid in the presence of at least one polymerization inhibitor requiring the introduction of oxygen and/or an inhibitor showing a higher effect in the presence of oxygen so as to stabilize the liquid, wherein the distillation is performed in the presence of NO2 gas at an oxygen/organic vapor ratio (W/W) of 0.02 to 3% and an NO2/organic vapor ratio (W/W) of 1×10−6 to 5×10−3% (i.e., 0.01 to 50 PPM).    [Document 1] KR 10-1996-0047606 (filed on Oct. 23, 1996)    [Document 2] KR 10-2002-7006584 (filed on May 23, 2002)
Documents 1 and 2 are quite different from the present invention in that the methods proposed in Documents 1 and 2 are directed to a distillation column including a dividing wall.